Radiant Heat System in 1050 sq ft Barndominium

rwoolwin

Hello,

I am building a 1050 sq ft barndominium in Spring 2021 and have been researching radiant heat systems. I will be doing an in-slab hydronic system. The main floor consists of a two car garage and a large family room. The family room stairs lead up to a 775 sq ft apt.

Primary question, will the apt above receive enough warmth or will I need another zone here for in-floor heat? I plan to insulate well and use good windows and am comfortable with 62-65F.

I am also looking for advice on what systems will be best for my project. I have gotten a quote from Stiebel Eltron on their Hydroshark preassembled systems and have also explored Viega. One major upside to Viega is that there is a mechanical company near me that could help with installation or services later down the road. I wouldn't have this option with the hydroshark system. I do not work in the trades so I am new to all of this, this being my reason for choosing the preassembled systems. Any advice on the best systems for this project is greatly appreciated.

The last factor I am struggling to decide on is LP or Electric Boiler. I am leaning towards electric because of energy efficiency and LP prices change so frequently but have read pros and cons of both. I plan to use my radiant heat system for my DHW as well so I will be using a heat integrator. Should this impact my decision on electric vs LP?

Again, I am an amateur at all of this and have been doing research for the past couple of weeks and just found this forum. There are so many posts in this forum that I am having difficulties finding ones that pertain to my basic questions..if you have threads that would be helpful..feel free to link them here.

Happy Holidays,

Ryan

Jamie Hall

Where is this project located? Unless you are located in the Pacific Northwest and plan to use a heat pump (much money!) the electric is going to be a lot more expensive to run. Further, unless -- again -- you are running a heat pump and are in the Pacific Northwest, the actual fuel efficiency of electric is much worse (30 to 40%) than LP (up to 95%, if you get and correctly install a nod/con boiler).

I strongly -- very very strongly -- recommend LP.

Now on heating the apartment -- no, the downstairs won't do it. You need to have radiant in that area as well.

On the "heat integrator" (not sure what that is?). There are two approaches which people use to running both domestic hot water and heating off the same appliance. The first is a group of boilers referred to as "Combi" boilers. These are arranged to heat both the domestic hot water and the heating system water, with the necessary controls and piping built in. They do work well, but very often the balance between the amount of heat required for the domestic hot water and the amount of heat for heating is poor (these are all "tankless" -- that is the heat the domestic hot water as it goes by, and that takes a big burner). The other approach, which is used very commonly, is to have the boiler correctly sized for the heating load, and to use hot water from it to heat a storage tank, called an indirect tank, as well. Except in rather rare situations, this works well.

After all that commentary, a word on design. The first step -- the very first step -- is to do a room by room heat loss for each space to be heated. There are various calculators for this -- I like the one Slant/Fin provides on its web site. Without doing this, you have no idea at all how big a boiler you need, nor do you have any idea at all as to how to lay out the radiant heating -- or even if radiant heating will provide enough heat.

Then, and only then, you can begin to think about how the system will be piped (loops, loop spacing, heat transfer plates in some cases, valving, pumps, etc. etc.) and how big a boiler you will need.

And once you have done that, you can begin to think about what materials you want to use.

Canucker

Don't forget Quebec @Jamie Hall They've got very cheap electricity too

Jamie Hall

Canucker said:

Don't forget Quebec @Jamie Hall They've got very cheap electricity too

True, oh sage... at least until Muskrat Falls comes on line...

hot_rod

Here is a quick cost comparison. A high efficiency LP boiler properly installed figure 90%.
When comparing electric, be sure it is the actual cost with all the fees applied, not just the first line Kw/ hr cost.

https://coalpail.com/fuel-comparison-calculator-home-heating

GroundUp

One thing I can say for sure, is to steer clear of the Hydro Shark systems in any and all variations. Their HQ is within an hour of me here and their stuff is peddled hard at a certain big box chain, everybody with the urge to save money tends to buy this junk and within a few years I'm there to replace at least some if not all of it as their "tech support" is nonexistent. I've even started building and marketing my own DIY kits to challenge them but using name brand ASME approved equipment instead of the questionable products in their kits.

With that said, electric is generally higher priced per BTU of output than LP is. If your power costs $.10/kwh, it would cost more per BTU until LP reaches north of approximately $2.50/gal. LP will also have a considerably higher upfront cost as well as added maintenance cost. Operating cost can all be calculated out with a heat loss analysis on the barndo and local utility prices. As Jamie mentioned, you will need some sort of supplemental heat for the upper level unless you keep it 80 degrees below. If you want to use it for both space heating and DHW, electric isn't much of an option for a single unit. An LP combi boiler could be a good choice if that's the goal, but again with the upfront and maintenance costs. Depending on your location and local utility costs, it may be more financially responsible to have 2 separate electric units for heating and DHW- especially if your electric provider offers a dual fuel rate and you can have an automatic backup heat source on LP such as a simple direct vent wall heater. For a building that size, personally I'd lean toward electric from a maintenance and longevity standpoint but that's with $.13 electricity and $1.25 propane here. Those both differ heavily nationwide

Ironman

Design is the first step and that starts with an accurate heat loss calc as Jammie mentioned.

There's no such thing as plug and play in doing this and I agree with GroundUp about a lot of the pre-assembled stuff. Even with good pre-assembled panels, the problem is that unless someone who can design specs the correct one, you end up with the wrong setup and then have to do it over or live with it. And most all plumbers and HVAC guys are clueless about proper design.

I'd highly recommend that you contact this man about designing it:
https://forum.heatinghelp.com/profile/Steve Minnich

rwoolwin

Thank you all for your input. The project is located in MI and the average propane cost this year was 1.70 a gallon. Electricity was ~13 cents kwh. Thanks for the fuel comparison calculator @hot_rod. LP appears to be the better option.

Jamie, the heat integrator is just another additional panel that they sell with the Hydroshark setup if you want DHW. Thanks for the advice on the heat loss calculator, I will run that through and see where it leads me.

I will likely be having a mechanical company help develop the system, they have worked with radiant heat systems for years and are pricing out a quote for me.

Sounds like this Steve Minnich guy is the real deal, may have to shoot him a message.

Jamie Hall

@Steve Minnich is definitely the real deal. One of the best for this type of system.

rwoolwin

Update:

using the slant/fin heat loss calculator I determined I will have an approximate total heat loss of 58,000 BTU/HR. On the main floor I will have a family room which is 365 sq ft and the heat loss for this room is about 10,400 BTU/HR. The 2 car garage next to the family room will be heated to about 55* and totaled a heat loss of about 13,200 BTU/HR. Finally, upstairs will be the main living space (775 sq ft), I calculated it all as one room since it will be 1-zone and is an open floor plan. It will be about 35,000 BTU/HR of heat loss.

So, from here this should help determine the PEX tubing size, spacing distance, and boiler. What are the best resources for determining the size and spacing? 

For the tankless water heater, I have heard good things about this Takagi: https://www.supplyhouse.com/Takagi-T-H3M-DV-N-T-H3M-DV-N-Indoor-Tankless-High-Efficiency-Condensing-Water-Heater-w-1-2-Gas-Supply-Lines-NG?gclid=EAIaIQobChMI39eXqbzW7QIVwdXACh03UQiGEAQYASABEgIfk_D_BwE

Any thoughts on this water heater for running both DHW and the radiant heat (3-zones)? It maxes out at 120,000BTU/HR

I still haven’t heard back from the mechanical company quote on this project but found out that my SIL’s dad built his own system over 20 years ago and her brother is an experienced mechanical engineer who also built his own radiant heat system so I may hire them to help me build my project. 

Jamie Hall

The unit you mention is a water heater, not a heating boiler. It is not meant for continuous operation, and if used as a heating boiler it will have a short and miserable life. Find and use an appropriately sized heating boiler to heat the radiant system. If possible, in fact, a mod/con, and use outdoor reset on it to maximize your efficiency and comfort.

Do not, whatever else you do, mix the domestic hot water and the radiant heating water. Radiant heating water typically is run at no more than 120 F -- ideal breeding temperatures for all sorts of unfortunate bacteria, molds, fungi, and the like. You don't want that in your shower or your coffee.

On the heating side, you are asking an awful lot of the radiant floors. A common figure is 20 BTUh per square foot. The family room is almost 30 BTUh per square foot, and if it is to be pretty much anything other than bare concrete or tile it just won't do it -- and even if it is, it will be pretty warm under foot. The upstairs space is 45 BTUh per square foot, and that just isn't feasible at any reasonable floor temperature m(you'd have to run the floor at over 100 F, more or less).

Bottom line on that: you will absolutely have to have more heat emitters. Panel radiators, baseboards... something anyway.

Time to drop back a bit and rethink this...

rwoolwin

Hi Jamie, I'm aware it is a tankless water heater and not a boiler. I just saw a lot of information for tankless water heaters and radiant floor heating. A lot of said information promotes the usage of tankless water heaters with radiant floor heating work but I do trust the judgement of all the professionals on this forum over promotions from companies who want to sell a product, that is why I am here.

I hadn't planned on mixing my DHW with radiant floor heat, I understand they run at completely different temperatures. In my mind I had a heat exchanger system separating the two as I have seen in some videos. Like I said, still in the planning stages, I have not purchased or built anything yet.

Can you send me information where you found the BTU per sq foot standards? I'm reading that 45BTU per sq ft is the max you can run without needing extra heat sources. I'm also wondering if the Slant/fin calculations aren't pinpoint to my exact build/insulation and the calculations are higher than they would normally be..the variable factors on the calculator are close but don't include exact R-values for each wall, window, etc. I should also note that I put the outdoor temperature at 1 degree F when calculating on the Slant/fin calculator. That is shooting low for MI. Of course we get temps that low and even lower, though it is more rare. Average winter temps are around 15-25 degrees F. So, long story short, I think these heat losses are the the very HIGH end of my calculations.

This should be an achievable project:

My bottom floor will be all bare concrete. This is a small building, I'm going to use 2X6 walls with 5 and 1/2" insulation, double pane windows, 2" rigid foam with vapor barrier beneath the concrete; I don't plan on going cheap anywhere with insulation. I'm not sure why radiant floor is out of the question?

In regards to the 775 sq ft apt area above my main floor (family room/garage), would it lower my BTU requirements by running two zones (sayyy 1 zone for the kitchen/living room and another zone for the bedroom/bathroom?)

I appreciate your quick replies and knowledge, but don't think radiant heat is out of the question. Where there is a will, there is a way.

Ironman

@rwoolwin
What Jamie has told you is spot on (he holds a PhD in engineering). A tankless water heater is the WRONG tool for the job. It’s not designed, controlled or approved for space heating. Without going into all the technical, reason with me: if a tankless water heater could take the place of a boiler, there would be no need to make boilers.

As far as floor output goes, 20 btus per square foot @ 120* SWT is about the most you can get using good heat transfer plates under a wood floor, depending upon the floor covering. You can get as high as 30 using Rehau Raupanels on top of the floor, but you’ll pay a premium for them.

These numbers come directly from a study that VA Tech did some years back. You can Google it.

I think your heat loss numbers of 45 btus per square foot are too high. I’ve done load calcs for 40 years and I’ve never seen anything close to that on a modern house.

Here’s a quick calc from Grundfos’ Hand book that’s easy and pretty accurate. It’s just simple math.

Jamie Hall

There is, more or less obviously, no real upper limit on how much heat a radiant floor can put out -- consider snowmelt systems! -- but there are two main considerations: how high a temperature can the flooring material support without damage, and how high a temperature can people in bare feet tolerate?

A very very rough back of the envelope constant for initial figuring is that the heat output in BTUh per square foot, very approximately, is 1.6 times the surface temperature minus 70. Using that rough estimate, and considering that a wood floor won't be happy at much over 85, 24 BTUh per square foot is about it. On the other hand, concrete or tile you could probably run up to 95 before people complained -- so 40 BTUh per square foot is not unreasonable. And, of course, that's net square feet -- anything covered by a rug or carpet, or under a cabinet (such as a vanity or kitchen cabinets) (or toilet or bathtub!) isn't usable.

With regard to the Slant/Fin calculator, it is known to be conservative -- that is, it will give figures which are unlikely to be exceeded -- but remarkably accurate. There is a good reason for that: the company doesn't want to be sued when someone uses the program and finds out that the actual heating load is higher than it calculated. However, if the input data are reasonable, it's usually within 10 percent. It is very important to remember that all of the input data -- to that or any other heat loss calculation -- are very poorly defined. Again, to refer to that 10 percent number, none of the various published insulation values (wherever they come from) are reliable beyond plus or minus 10 percent -- that is, if a wall material is rated at an R value of 6, for instance, the real value is likely to be anywhere between 5.4 and 6.6. Then, for an assembly, to get even remotely closer than that you have to account for heat conduction bridges (such as wall studs!) and a raft of other variables. I wouldn't be too concerned if you can't find exact values -- since they won't be exact anyway.

The biggest variable lies in the choice of design outdoor temperature and desired indoor temperature. There you may run into a conflict between what you know you would be perfectly happy with -- perhaps 55 on one of those 0 degree nights! -- and what the building code may require, which is likely to be 70 degrees on the "design day". The latter may not be a problem where you are -- codes vary from town to town, never mind state to state -- nor may it be a problem if you don't need a mortgage or a certificate of occupancy, or desire to have the option to sell down the road sometime. That's for you to consider and evaluate, I can't help you on that.

And no, it won't help to rearrange the piping into multiple loops -- whatever works to drive the floor to the target temperature.

Good luck!

rwoolwin

@Jamie Hall and @Ironman thank you both for the feedback and information. The heat loss calculation chart was very helpful and is in the same range as the Slant/Fin calculations-though the chart from the book uses 0 degrees at the outdoor temp and Jamie made a good point about desirable indoors temps as outdoor temps drop-most people aren't shooting for 70 degrees indoors when its 0 out (well anyone who wants a reasonable heat bill anyway). I shot for 65 F when doing the calculations (and still have a pretty high BTUs for the Family room due to the size of the room (365 sq ft) and large windows (may have to rethink a different size on the windows). As mentioned, this room will be bare concrete so I can run pretty warm temps through it and shoes or slippers will likely be worn down here. Not as worried about this room as the upstairs.

I still haven't chosen a type of flooring for the above apt and don't plan on using wood flooring but certainly need to redo the math for the heat loss in this living space, I agree that 45BTU heat loss up here seems too high and that there should be a way to do radiant heat up here as well.

Again, thanks for all of your replies Jamie.

rwoolwin

After completing the calculations again (using Slant/fin) with closer attention to detail and separating the rooms more accurately in the above apt, I came up with: Family room (65* indoor/5* outdoor) 8246 BTU/345 sq ft= about 25 btu/sq ft. Garage is tricky because of the doors but came up with: (55* indoor/5* outdoor) 27,050/685 sq ft= about 39.5 btu/sq ft. Upstairs rooms (65* indoor/5* outdoor) living room=6100 BTU/191 sq ft= about 32 btu/sq ft. Kitchen/Dining=4847 BTU/222 sq ft= about 22 btu/sq ft. Bedroom=7500 BTU/228 sq ft=about 33 btu/sq ft. Now I have closets and a bathroom all along the back side of these 3 rooms. I measured this all as one space, there are no windows. Came up with 2814BTU/180 sq ft=about 16 btu/sq ft.

That puts my total heat los per sq foot right around 30 for the whole build. This all assuming I did it right the second time I’m still above the suggested 20-25 BTUs. Other sources say 25-35 is a good Number. 

Jamie Hall

With careful attention to the loop spacings and layout, you may be able to just about make it. You will probably want to adjust the loop spacings in the various areas so that you don't overheat the areas -- like the kitchen/dining -- which don't require as much heat.

I'd also want to zone at least the garage separately, as it can run at a higher floor temperature.

kenjohnson

You asked for links from others who have designed/installed radiant systems, so here is mine: https://forum.heatinghelp.com/discussion/163346/would-like-some-feedback-on-my-radiant-design-plans#latest

First, I will tell you that you can definitely design and install all or most of this yourself if you can do the basic math for heat loss calculations and can use basic tools. I left the plumbing connections to others (I know what I am good at). Installing the plates takes time, but is not hard. Running the PEX is at least a three-person job. What I learned doing all this is covered in my post. I am technical, so I basically did all my own calculations and radiant plate and PEX layout design with some feedback from this forum. Having said that, grinding protruding nails off of old floorboards (necessary for a renovation, probably not necessary for new construction), installing plates and running PEX was a a real grind, so know that going in.

Second, I can tell you that this is absolutely the most comfortable heat I can imagine having - better than cast-iron radiators. It was worth all the time and money I put into doing this. I strongly recommend it. I'm looking forward to moving into this house and not just working inside it.

If you are not confident on the design side and can find someone to do the design work for you, that is a great option. Make sure they specify where to put every plate using actual floor and rafter layouts. I frankly would have loved to have had someone do all this for me, but in doing it myself I learned a lot and that helped me when I had to improvise a bit during the install.

My system is geothermal ground-source heat pump heated (electric). If I paid wintertime retail rates for electricity here in Central NY (I have net metered solar PV), it would cost me about $400 to heat this 1750 square foot home at 10 cents/kWh (yes, that is the all in rate - don't believe everything you hear about high NY electric prices). The downside is that the upfront cost of this system is really high - you pay a lot early to save a lot later.

I've had requests for pictures and what not and I just have not had time to put them in my post. But I am happy to answer any questions on what I did and why.